1. Field of the Invention
This invention relates to an improvement in a radiation image read-out apparatus for reading out a radiation image stored in a stimulable phosphor sheet by exposing the stimulable phosphor sheet to stimulating rays which cause it to emit light in proportion to the radiation energy stored and photoelectrically detecting the emitted light.
2. Description of the Prior Art
When certain kinds of phosphors are exposed to a radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays or ultraviolet rays, they store a part of the energy of the radiation. Then, when the phosphor which has been exposed to the radiation is exposed to a stimulating ray such as visible light, light is emitted from the phosphor in proportion to the stored energy of the radiation. A phosphor exhibiting such properties is referred to as a stimulable phosphor.
As disclosed in U.S. Pat. Nos. 4,258,264, 4,276,473 and 4,315,318, 4,387,428 and Japanese Unexamined Patent Publication No. 56(1981)-11395, it has been proposed to use a stimulable phosphor in a radiation image recording and reproducing system. Specifically, a sheet comprising the stimulable phosphor is first exposed to a radiation passing through an object to have a radiation image stored therein, and is then scanned with stimulating rays such as a laser beam which cause it to emit light in proportion to the radiation energy stored. The light emitted from the stimulable phosphor sheet when the sheet is exposed to the stimulating rays is guided by a light transferring means and photoelectrically detected and converted by a photodetector to an electric image signal. By use of the electric image signal, a light beam is modulated to reproduce a visible radiation image on a recording medium such as a photographic film.
As the light transferring means used in the aforesaid radiation image recording and reproducing system, a light transferring means consisting of a light guiding sheet is disclosed, for example, in U.S. Pat. No. 4,346,295. The light transferring means is fabricated by forming an acrylic light guiding sheet or the like so that one end face (light input face) is linear and the other end face (light output face) matches the shape of the light receiving face of a photodetector. The light output face is closely contacted with the photodetector. In general, between the light output face of the light transferring means and the photodetector is positioned a filter for passing only the light emitted from the stimulable phosphor sheet when the sheet is exposed to stimulating rays. The light output face of the light transferring means, the filter, and the light receiving face of the photodetector are closely contacted with each other. That is, the light transferring means, the filter, and the photodetector are closely contacted and formed integrally with each other. In some cases, instead of using the filter, the light transferring means is colored so that it acts in the same manner as a filter.
However, when the light transferring means, the filter and the light receiving face of the photodetector (or the light transferring means and the light receiving face of the photodetector when the filter is not used) are closely contacted and formed integrally with each other, it is impossible to detach the photodetector from the light transferring means and the filter. Therefore, when the photodetector, which has a much shorter service life than the light transferring means and the filter, has to be replaced, the light transferring means and the filter (or the light transferring means in the case where the filter is not used) must also be replaced together with the photodetector. This is very disadvantageous from the economical viewpoint.